The Bean Leaf Beetle PDF Download

The bean leaf beetle, Cerotoma trifurcata (Förster) (Coleoptera: Chrysomelidae), has recently become a major pest of soybean (Glycine max (L.) Merrill) in North America. With the possibility of further economic losses, an understanding of the potential indirect and direct effects of climate change on the severity of this pest is required. The plant-mediated effects of elevated CO2 on bean leaf beetle fecundity were examined. While non-nitrogen-fixing plants generally show decreases in leaf carbon to nitrogen ratio under elevated CO2, which can negatively impact insect herbivores, there was no change in the carbon to nitrogen ratio of soybean leaves, a nitrogen-fixer, in this study. The lack of change in leaf carbon to nitrogen ratio under elevated CO2 may explain the absence of a treatment effect on bean leaf beetle fecundity in one year of the experiment. However, in the second year, there was an increase in bean leaf beetle fecundity under elevated CO2. Using a multi-year field experiment, I examined the potential direct effects of climate change, namely the impacts of warmer winters on bean leaf beetle overwintering survival and spring emergence. Under increased temperatures, bean leaf beetles emerged 10 to 20 days earlier in the spring which could allow for an additional generation during the growing season. Higher temperatures also led to decreased survival. I developed a bioclimatic envelope model for the bean leaf beetle to examine the direct effects of climate change on a broader scale. I combined this model with the soybean climate envelope to predict the future potential distribution of the bean leaf beetle based both on climate and host plant availability. Since soybean generally has narrower tolerances than the bean leaf beetle, incorporation of host plant availability had a substantial impact on predictions of bean leaf beetle distribution. The inclusion of climate projections from multiple general circulation models (GCMs) and scenarios was a source of variability in our predictions, with only two of the three GCMs predicting further expansion of the bean leaf beetle into Canada.